Every field of science has its favorite anniversary. For physicists, this is Newton's Principles, a book from 1687, which introduced the laws of motion and gravity. Biologists celebrate the Darwinian Origin of Species (1859) and his birthday (1809). Astronomers celebrate the year 1543, because it was then that Copernicus placed the sun in the center of the solar system. As for chemistry, not a single reason for the celebration surpasses the appearance of the periodic table of elements created 150 years ago in March by the Russian chemist Dmitry Ivanovich Mendeleev.
Periodic table has become the same forchemical students like calculators for accountants. It contains all the science in a little over a hundred squares containing symbols and numbers. It lists the elements that make up all terrestrial substances, grouped in such a way that it was possible to identify patterns in their properties, to determine the purpose of chemical research, both in theory and in practice.
Periodic table is undoubtedly the most important concept in chemistry.
Periodic table looked like a specialthe table, but he himself wanted it to reflect the deep scientific truth that he discovered: the periodic law. His law revealed deep family relationships between known chemical elements — they exhibit similar properties at regular intervals (or periods), if arranged in atomic weight order — and allowed Mendeleev to predict the existence of elements that have not yet been discovered.
"Before the promulgation of this law, chemicalthe elements were merely fragmentary, random facts in Nature, ”stated Mendeleev. "For the first time, the law of periodicity allowed us to see undiscovered elements at a distance that was previously inaccessible for chemical vision."
Periodic Table not only predictedthe existence of new elements. She confirmed then still controversial belief in the reality of atoms. She hinted at the existence of a subatomic structure and foresaw the mathematical apparatus underlying the rules governing matter, which ultimately manifested themselves in quantum theory. His table completed the transformation of chemical science from medieval magical mysticism of alchemy into a field of modern scientific rigor. The periodic table symbolizes not so much the constituents of a substance as logical consistency and fundamental rationality of science as a whole.
How the periodic table was created
Legend has it that Mendeleev conceived and createdown table in one day: February 17, 1869, according to the Russian calendar (for most of the world, this is March 1). But this is most likely an exaggeration. Mendeleev thought about the grouping of elements over the years, and other chemists several times considered the concept of connections between elements in previous decades.
In fact, the German physicist Johann WolfgangDobereiner noticed the features of grouping elements back in 1817. In those days, chemists had not yet fully understood the nature of atoms, as described by John Dalton’s atomic theory in 1808. In his “new system of chemical philosophy,” Dalton explained chemical reactions, suggesting that every elemental substance consists of an atom of a certain type.
Dalton suggested that chemical reactionsproduced new substances when atoms are separated or joined. He believed that any element consists solely of one type of atom, which differs from the others in weight. Oxygen atoms weighed eight times more than hydrogen atoms. Dalton believed that carbon atoms are six times heavier than hydrogen. When elements are combined to create new substances, the amount of reactants can be calculated taking into account these atomic weights.
Dalton was wrong about some masses - oxygenin fact, 16 times heavier than hydrogen, and carbon 12 times heavier than hydrogen. But his theory made the idea of atoms useful, inspiring a revolution in chemistry. Accurate measurement of the atomic mass has become a major problem for chemists over the next decades.
Reflecting on these scales, Dobereiner noted thatcertain sets of three elements (he called them triads) show an interesting connection. Bromine, for example, had an atomic mass somewhere between the masses of chlorine and iodine, and all three elements showed similar chemical behavior. Lithium, sodium and potassium were also a triad.
Other chemists have noticed connections between atomicmasses and chemical properties, but only in the 1860s did atomic masses become well enough understood and measured to develop a deeper understanding. The English chemist John Newlands noted that the arrangement of known elements in order of increasing atomic mass led to a repetition of the chemical properties of every eighth element. He called this model the “octave law” in the 1865 article. But the model of Newlands did not keep well after the first two octaves, which made critics suggest that he arrange the elements in alphabetical order. And as Mendeleev soon realized, the relationship between the properties of the elements and the atomic masses was a little more complicated.
Organization of elements
Mendeleev was born in Tobolsk, in Siberia, in 1834was the seventeenth child of his parents. He lived a vibrant life, pursuing different interests and traveling along the road to outstanding people. While receiving higher education at the Pedagogical Institute in St. Petersburg, he almost died from a serious illness. After graduation, he taught at secondary schools (this was necessary to receive a salary at the institute), while at the same time studying mathematics and natural sciences to obtain a master's degree.
He then worked as a teacher and lecturer (and wrote scientific papers) until he received a scholarship for an extended research tour in the best chemical laboratories in Europe.
Back in St. Petersburg, he was withoutwork, therefore, wrote an excellent guide to organic chemistry in the hope of winning a large cash prize. In 1862, he won the Demidov Prize. He also worked as an editor, translator and consultant in various chemical fields. In 1865, he returned to research, received a PhD and became a professor at St. Petersburg University.
Soon after, Mendeleev began teachinginorganic chemistry. Preparing to master this new (for him) field, he remained dissatisfied with the available textbooks. Therefore, I decided to write my own. The organization of the text required the organization of the elements, so the question of their best location was always on his mind.
By the beginning of 1869, Mendeleev had achieved sufficientprogress to understand that some groups of similar elements showed a regular increase in atomic masses; other elements with approximately the same atomic masses had similar properties. It turned out that the ordering of elements according to their atomic weight was the key to their classification.
According to Mendeleev’s own words, hestructured his thinking by writing each of the 63 then known elements on a separate card. Then, through a kind of chemical solitaire game, he found the pattern he was looking for. Placing the cards in vertical columns with atomic masses from low to higher, he placed elements with similar properties in each horizontal row. Periodic table of Mendeleev was born. He sketched a draft version on March 1, sent it to print and included it in his textbook, which was soon to be published. He also quickly prepared a paper for presentation to the Russian Chemical Society.
"Elements ordered by their atomic sizemasses, show clear periodic properties ", wrote Mendeleev in his work. "All the comparisons I made led me to the conclusion that the size of the atomic mass determines the nature of the elements."
Meanwhile, German chemist Lothar Meyer alsoworked on the organization of the elements. He prepared a table similar to the Mendeleev one, perhaps even earlier than Mendeleev. But Mendeleev published his first.
However, much more important than winningover Meyer, was how Mendeleev used his table to make bold predictions about undiscovered items. In preparing his spreadsheet, Mendeleev noticed that some of the cards were missing. He had to leave empty spaces so that the known elements could align properly. During his lifetime, three empty places were filled with previously unknown elements: gallium, scandium and germanium.
Mendeleev not only predicted the existence of theseelements, but also correctly described their properties in detail. Gallium, for example, discovered in 1875, had an atomic mass of 69.9 and a density six times that of water. Mendeleev predicted this element (he called it aluminum), only by this density and atomic mass of 68. His predictions for ecacarium closely corresponded to Germany (discovered in 1886) by atomic mass (72 predicted, 72.3 in fact) and density. He also correctly predicted the density of germanium compounds with oxygen and chlorine.
The periodic table became prophetic. It seemed that at the end of this game this elementary solitaire would reveal the secrets of the universe. At the same time, Mendeleev himself was a master in using his own table.
Mendeleev's successful predictions brought himthe legendary status of a master of chemical magic. But today historians argue whether the discovery of the predicted elements has consolidated the adoption of its periodic law. Adoption of the law could be more related to its ability to explain the established chemical bonds. In any case, the predictive accuracy of Mendeleev, of course, drew attention to the merits of his table.
By the 1890s, chemists widely recognized his law.as a milestone in chemical knowledge. In 1900, the future Nobel laureate in chemistry, William Ramsay, called it "the greatest generalization ever carried out in chemistry." And Mendeleev did it without knowing how.
In many cases in the history of science are greatpredictions based on new equations turned out to be true. Somehow, mathematics reveals some natural secrets before the experimenters discover them. One example is antimatter, the other is the expansion of the universe. In the case of Mendeleev, the predictions of new elements arose without any creative mathematics. But in fact, Mendeleev discovered a deep mathematical map of nature, since his table reflected the meaning of quantum mechanics, the mathematical rules governing atomic architecture.
In his book, Mendeleev noted that “internalthe differences of matter that constitutes atoms can be responsible for periodically recurring properties of elements. But he did not adhere to this line of thinking. In fact, for many years he thought about how important atomic theory is for his table.
But others were able to read the inner message.tables. In 1888, the German chemist Johannes Wislitzen declared that the periodicity of the properties of elements ordered by mass indicates that atoms consist of regular groups of smaller particles. Thus, in a sense, the periodic table did indeed foresee (and provided evidence) the complex internal structure of atoms, while no one had any idea how the atom actually looked like or whether it had any internal structure at all.
By the time Mendeleev died in 1907, scientistsknew that the atoms are divided into parts: electrons that carry a negative electric charge, plus some positively charged component that makes the atoms electrically neutral. The key to how these parts line up was the discovery of 1911, when the physicist Ernest Rutherford, who works at the University of Manchester in England, discovered the atomic nucleus. Shortly thereafter, Henry Mosley, who worked with Rutherford, demonstrated that the amount of positive charge in the nucleus (the number of protons that it contains, or its “atomic number”) determines the correct order of the elements in the periodic table.
Atomic mass was closely related to atomic numberMosley is close enough so that the ordering of elements by mass in only a few places differs from the ordering in number. Mendeleev insisted that these masses were wrong and needed to be re-measured, and in some cases turned out to be right. Only a few discrepancies remain, but the atomic number of Mozley perfectly lay down in the table.
At about the same time, Danish physicist Niels Bohr realized that quantum theory determines the arrangement of the electrons surrounding the nucleus, and that the most distant electrons determine the chemical properties of an element.
Similar arrangements of external electrons will beRepeat periodically, explaining the patterns that the Periodic Table originally revealed. Bohr created his own version of the table in 1922, based on experimental measurements of electron energy (along with some tips from periodic law).
Bohr table added elements opened since 1869years, but it was the same periodic order, open Mendeleev. Having no idea about quantum theory, Mendeleev created a table reflecting the atomic architecture dictated by quantum physics.
Bora’s new table was neither the first northe latest version of the initial design of the Mendeleev. Hundreds of versions of the periodic table have since been developed and published. The modern form - in horizontal design, unlike the original vertical version of Mendeleev - became widely popular only after the Second World War, thanks in large part to the work of the American chemist Glenn Seaborg.
Seaborg and his colleagues have created several newelements synthetically, with atomic numbers after uranium, the last natural element in the table. Seaborg saw that these elements, transuranic (plus the three elements that preceded uranium), required a new row in the table that Mendeleev had not foreseen. The Seaborg table added a row for those elements under a similar series of rare earth elements that also had no place in the table.
The contribution of Seaborg in chemistry brought him the honor to nameown element - siborgiy with number 106. This is one of several elements named after famous scientists. And in this list, of course, there is an element 101, opened by Seaborg and his colleagues in 1955 and named Mendelevy - in honor of the chemist, who, above all others, deserved a place in the periodic table.
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